Synthesis and Radical Polymerization of a Methacrylate Monomer Containing a NLO-phore 4-(p-Oxyphenyliminomethylidene)-4' -nitrostilbene

NLO- 발색단인 4-0 -옥시페닐이미노메틸리 덴)- 4'- 니트로스틸벤을 포함하는 메타크릴레이트 단량체의 합성 및 라디칼중합

李科淵* •李賢珠•金武容

인제대학교 화학과

(1995. 11. 14

Synthesis and Radical Polymerization of a Methacrylate Monomer Containing

a NLO-phore 4-Oxyphenyliminomethylidene)-4 ,- nitrostilbene

Ju-Yeon Lee*, Hyun-Ju Lee, and Moo-Yong Kim Department of Chemistry, Inje University, Kimhae 621-749, Korea

(Received November 14, 1995)

Functional materials of nonlinear optical (NLO) activity based on organic compounds have long been the subject of curiosity and have caused re­

cent intrest because of their potential applications in the field of telecommunications, optical signal processing, optical switching, etc) It is well known that organic and polymeric materials with highly dipolar electronic systems exhibit NLO properties.

The organic materials seem to be superior because of their higher nonlinear optical activity and faster response time than the inorganic ones. Among the organic materials the NLO polymers are receiving great attention, mainly because they offer many advantages such as mechanical endurance, light weight, chemical resistance, and good processabi­

lity to form optical devices.2 A potentially NLO polymer must contain a highly polarizable n-elect- ronic systems and these polymers have to be me­

chanically very strong. There are tremendous cha­

llenges in designing and synthesis of polymers of large NLO effects. Polyesters,3 polyurethanes,4 pol­

yamides,5 and poly(phenyleneethynylenes)6 contai­

ning the chromophoric main chain were prepared.

Various polymers with the NLO-phores in the side chain such as poly(meth)acrylates,7 polystyrene,8 and poly(alkyl vinyl ethers)9 were also reported.

Robello10 prepared polyacrylates bearing aminoni­

trostilbene and azo dyes in the side chain. Recen­

tly polymethacrylates containing mesogenic (car- bazoylmethylene)aniline and 4- nitrobenzylidenea­

niline groups in the side chain were al

reported by Uryu

"However, examples of NLO-poly- mers with the chromophoric side chain composed of three conjugated phenyl groups are seldom found in the literature. Thus, it is of interest to prepare polymethacrylate containing three conju­

gated phenyl groups as the NLO-phore in the side chain. In this work we prepared polymethacrylate with the NLO-phore 4- (p -oxyphenyliminomethyli- dene)-4f-nitrostilbenet which is presumably effec­

tive chromophore for second-order nonlinear opti­

cal applications in the side chain. The present re­

port describes the synthesis and radical polymeri­

zation of 4-{/)-(2-methacryloyloxyethoxy)phenyli- minomethylidene} -4/-nitrostilbene 6.

4f-Methyl-4-nitrostilbene 1 was synthesized by the condensation of 4-nitrophenylacetic acid with />-tolualdehyde according to a literature procedure12 and recrystallized from ethanol. Bromination of compound 1 by ^-bromosuccinimide (NBS) yiel­

ded 4,-bromomethyl-4-nitrostilbene 2. 4f-Nitro-

4-stilbenecarboxaldehyde 3 was synthesized, acco-

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153

piperidine 140 °C

NBS, BPO CC

、

2

ICHaCH20H, DMF K2CO318O°C '

Scheme 1.

rding to a known method13 by oxidation of the corresponding benzyl bromide 2. 4-(/>-Hydroxy- phenyliminomethylidene)-4, - nitrostilbene 4 was prepared by the reaction of - nitro-4- stilbenecar- boxaldehyde 3 with /)-aminophenol, and reacted with 2-iodoethanol to yield 4-|/)-(2-hydroxye- thoxy)phenyliminomethylidene} -4,-nitrostilbene 5.

The methacrylate 6 was synthesized from methac­

ryloyl chloride and compound 5 following establi­

shed literature procedure.11 In dilute chloroform solution, the title compound was obtained in mo­

derate yield (Scheme 1). The chemical structures of the compounds were confirmed by 'H NMR, IR (Fig, 1(a)), UV-Vis, and elemental analyses.

Monomer 6 shows olefinic protons at 8=5.53~

5.78 (m, 1H, vinylic) and 8=5.93〜6.20 (m, 1H,

Fig. 1. IR spectra of monomer 6 (a) and polymer 7 (b).

vinylic) in its 'H NMR. The same monomer sample showed strong absorption bands at 1710, 1592, and 1338 cm-1 indicating the presence of carbonyl, olefinic, and nitro groups, respectively as shown in Fig. 1(a). Compound 6 showed strong uv absor­

ption bands near 353 nm by the chromophore p- oxy-A^-(4~nitrostilbenzylidene)aniline in the side chain measured in chloroform. Monomer 6 is mo­

derately soluble in common organic solvents such as acetone and DMSO, but is slightly soluble in ethanol and diethyl ether.

/>-(2-Methacryloyloxyethoxy)-A^-(4-nitrostilben- zylidene)aniline 6 was polymerized with AIBN as radical initiator to obtain the polymer 7 (Scheme 2). Polymerizations were carried out in Y-butyro­

lactone solutuin at 65 t. The polymerization re

Its are summarized in Table 1.

Monomer 6 was quite reactive toward radical initiator and polymerized readily. In most cases, conversions were quite high (>90%) as shown in Table 1. The chemical structure of the polymer 7 was identified by IR (Fig. 1(b)), UV-Vis spectra and elemental analyses. The IR spectrum confir­

med the chemical structures, exhibiting all the ab­

sorption bands attributable to the functional

groups comprising the polymer. The polymer 7

showed strong absorption bands at 1717, 1584, and

Table 1. Free radical p

ymerization of 6 by AIBN in Y-butyrolactone at 65 aC

Monomer0 Monomer/

Solvent (mol/1 L)

Initiator to Monomer

(mol%)

Time Yield (h) (%)

6 0.42 1.0 24 92

6 0.33 1.0 20 91

6 0.50 0.8 24 90

6 0.38 2.0 20 92

6=4-{/>-(2-methacryloyloxyethoxy)phenyliminome- thylidene} -4,-nitrostilbene.

Table 2. Thermal properties of polymer 7

Polymer

Degradation temp.

Residue^ at 5%- 20%- 40%- 700 °C, % loss loss loss

7 165 308 400 484 3.44 Scheme 2.

1333 cm1 in its IR spectrum indicating the prese­

nce of carbonyl, olefinic, and nitro groups, respec­

tively as shown in Fig. 1(b). The same polymer sample showed strong uv absorption bands near 353 nm by the chromophore ^-oxy-Ar-(4-nitrostil- benzylidene)aniline in the side chain as in the mo­

nomer 6. These spectral evidences indicate that the radical polymerization proceeded cleanly via vinyl type polymerization. Cross-linking through the internal double bonds are obviously not favo­

red for steric reasons. The polymer 7 was not very soluble in common organic solvents, probably due to the presence of polar and bulky pendant group.

The thermal behavior of the polymer was inves­

tigated by thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) to deter­

mine the thermal degradation pattern and glass transition temperature (TK). The results are sum­

marized in Table 2. TGA thermograms showed tri­

ple phase degradation patterns, probably due to the presence of three benzene rings in the pen­

dant group. The polymer showed a thermal stabi­

lity up to 300 t in TGA thermogram. The Tg va­

lues of the polymers obtained from DSC thermog­

rams were around 166 t：, which is acceptable for NLO device applications. These Tg values are hi-

^Determined from DSC curves measured on a DuPont 910 differential scanning calorimeter with a heating rate of 10 M/min under nitrogen atmosphere. ^Deter- mined from TGA curves measured on a DuPont 951 thermogravimetric analyzer with a heating rate of 10 t/min under nitrogen atmosphere.

gher than those for poly(methyl methacrylate) (105 M), probably due to the presence of polar and bu­

lky pendant group.

In summary, a new methacrylate monomer 6 containing a highly dipolar electronic system com­

posed of three conjugated phenyl groups was pre­

pared and polymerized radically. The novel poly­

methacrylate 7 contains 4-(/>-oxyphenyliminome- thylidene)-4z-nitrostilbene, which is presumably effective chromophore for second-order nonlinear optical applications. The substituted polymethacry­

late 7 was not soluble in common organic solvents, probably due to the presence of polar and bulky pendant group. The polymer showed a thermal stability up to 300 °C, showing Tg peaks around 166 t. Copolymerization with other monomers such as methyl methacrylate to increase solubility and measurements of NLO properties are in prog­

ress, and the full accounts of the work will be

reported later.

NLO-

155

EXPERIMENTAL

Materials. 2-Iodoethanol,

tolualdehyde, 4- nitrophenylacetic acid, 4-aminophenol (Aldrich) were used as received. Carbon tetrachloride was refluxed with phosphorus pentoxide under nitro­

gen and distilled. Sodium iodide was dried for 4 h at 100 fc under vacuum. Acetone was purified by drying with anhydrous potassium carbonate, fo­

llowed by distillation under nitrogen. Dimethyl su- Ifoxide (DMSO) was dried over 4 A molecular sie­ o ves for several days and distilled under vacuum.

Dimethylformamide (DMF) was purified by drying with anhydrous calcium sulfate, followed by distillation under reduced pressure. Chloroform was washed with water to remove the ethanol, dried with anhydrous potassium carbonate, reflu­

xed with anhydrous calcium chloride, and distilled.

Methacryloyl chloride was distilled and used im­

mediately. Triethylamine was refluxed over potas­

sium hydroxide and distilled. Y-Butyrolactone was dried with anhydrous magnesium sulfate and frac­

tionally distilled under nitrogen. Piperidine was dried with calcium hydride and fractionally distil­

led. a,a' -Azobisisobutyronitrile (AIBN) was recry­

stallized from methanol and dried under reduced pressure at room temperature.

Measurements. IR spectra were taken on a Hi­

tachi Mod

260-30 infrared spectrophotometer.

NMR spectra were obtained on a Varian EM 360L NMR spectrometer (60 MHz). UV-VIS spec­

tra were obtained on a Kontron UVikon 860 spect­

rophotometer. Elemental analyses were performed using a Perkin-Elmer 2400 CHN elemental analy­

zer. The glass transition temperatures (Tg) were measured on a DuPont 910 differential scanning calorimeter in a nitrogen atmosphere. DuPont 951 thermogravimetric analyzer with a heating rate of 10 t/min up to 700

was used for the thermal degradation study of polymers under nitrogen.

Melting points were measured in Buchi 530 mel­

ting point apparatus and are corrected. Viscosity values were obtained by using

Cannon-Fenske viscometer.

Preparation of 4,-methyl-4-nitrostilbene (1).

Compound 1 was prepared by a known method29

from /)-tolualdehyde and 4-nitrophenylacetic acid, and recrystallized from ethanol. Mp 139~140 °C.

NMR (acetone~d6) 8 2.33 (s, benzylic 3H), 7.04~7.95 (m, aromatic 8H), 8.05—8.35 (d, aroma­

tic 2H). IR (neat) 3075, 3015 (w, =C-H), 1626, 1592, (s, C = C), 1512, 1347 (vs, N = O) cm \ Anal.

Calcd for C15H13NO2: C, 75.30; H, 5.47; N, 5.86.

Found: C, 75.42; H, 5.51; N, 5.90.

Preparation of 4,-bromomethyl-4-nitrostilbene (2). 4,-Methyl-4-nitrostilbene (13.6 g, 0,057 mol), A^-bromosuccinimide (10.7 g, 0.060 m

and ben­

zoyl peroxide (0.14 g) were dissolved in 90 mL of CC14 under a nitrogen atmosphere. The mixture was refluxed with vigorous stirring at 85 t for 12 h under nitrogen. The resulting solution was cooled to room temperature, filtered with suction, and rinsed with 30 mL of CC14. The yellow solid on the filter was washed thoroughly with water to remove succinimide. The product was recry

tal- lized from ethanol yielded 14.1 g (78% yield) of pure product 2. Mp 127—128 °C. 'H NMR (ace­

tone-d6) 8 2.33 (s, benzylic 3H), 7.04~7.95 (m, aro­

matic 8H), 8.05~8.35 (d, aromatic 2H). IR (neat) 3020 (w, =C-H), 1628, 1586 (s, C=C), 1508, 1328 (vs, N=O) cm1. Anal. Calcd for Ci5H12BrNO2： C, 56.63; H, 3.80; N, 4.40. Found: C, 56.56； H, 3.76;

N, 4.45.

Preparation of 4,-nitro-4-stilbenecarboxaldeh- yde (3). A mixture of 11.5 g (0.036 mo) of 4f-bro- momethyl-4-nitrostilbene and 10.5 g (0.054 mol) of potassium chromate in 55 mL of DMSO was refluxed with vigorous stirring at 115 °C for 2 h under nitrogen. Extraction was performed on the resulting black solution thrice with 250 mL of die­

thyl ether. The organic layer was concentrated by distillation of the solvent. The residue was preci­

pitated into 300 mL of water contained in a round bottomed flask, which was stirred. The precipita­

ted yellow product was filtered with suction and washed successively twice with 100 mL of water and 100 mL of n-hexane. Thus obtained product was recrystallized from ethanol yielded 7.3 g (80%

yield) of pure product 3. Mp 199—200 °C (dec).

】

H NMR (acetone-d6) 8 9.99 (s, -CHO), 7.18-8.37

(m, aromatic 10H). IR (neat) 1687 (vs, C = O), 1598,

1565 (vs, C = C), 1505, 1334 (vs, N = O) cm=

UV/Vis (chloroform)

max = 354 nm, €=23630. Anal.

Anal. Calcd for C15HUNO3: C, 71.14： H, 438; N, 5.53. Found: C, 71.21; H, 4.36; N, 5.56.

Preparation of 4-<p-hydroxyphenyliminomethyli- dene)-4, -nitrostilbene (4). Compound 4 was pre­

pared by a known method11 from 4-nitrobenzalde- hyde and 4-aminophenol in absolute ethanol, and recrystallized from acetone. Yield = 90%; mp 215~

216 fc (dec).NMR (DMSO-d6) 8 6.77〜

7.46 (m, aromatic 4H), 7.66 (s, aromatic 1H), 7.76~

8.19 (m, aromatic 6H), &22~8.52 (d, aromatic 2H)(

8.75 (s, -N = CH-)t 9.48 (s, -OH); IR (KBr) 3420 (s, O-H), 1614, 1578 (C = C), 1498, 1338 (vs, N = 0) cm I UV/Vis (chloroform) Max=356 nmt e = 26300. Anal. Calcd for C 2 i H16N2 O 3 : C, 73.24; H, 4.68; N, 8.13. Found: C, 73.28; H, 4.64; N, 8.16.

Preparation of 4- (p-(2- hydroxyethoxy)phenyli- minomethylidene) -4r-nitrostilbene (5).

droxyphenyliminomethylidene)-4,-nitrostilbene (4.82 g, 0.014 m

anhydrous potassium carbonate (5.80 g, 0.042 mol), and 2-iodoethanol (3.58 g, 0.021 mol) were dissolved in 25 mL of dry DMF under nitrogen. The mixture was refluxed in an oil bath kept at 80 °C for 10 h under nitrogen. The resul­

ting solution was cooled to room temperature, di­

luted with 100 mL of water, stirred, filtered, and the obtained brown product was washed with 100 mL of water. Thus obtained product was recrystal­

lized from ethanol yielded 3.92 g (72% yi

d) of pure product 5. Mp 172—173 (dec). NMR

①MSO-dQ 8 347〜3.89 (m, 2H, -CH2-O-), 3.90- 4.15 (m, 2H, Ph-O-CH2-), 4.16-4.61 (m, 1H, -OH), 6.65〜8.89 (m, 15H, aromatic); IR (KBr) 3538 (s, O-H), 3078 (=C-H), 2954, 2928 (w, C-H), 1618, 1588 (vs, C = C), 1508, 1342 (vs, N = O) cmf UV/Vis (chloroform)

max=355 nm, e=29320. Anal.

Calcd for C23H2oN204: C, 71.12; H, 5.19; N, 7.21.

Found: C, 71.18; H, 5.24; N, 7.28.

Preparation of 4- (p-(2-methacryloyloxyethoxy) phenyliminomethylidene) -4r-mtrostilbene (6). A solution of methacryloyl chloride (2.09 g, 20 mmol) in 10 mL of chloroform was slowly added dropwise to a solution containing 4-

hydroxyethoxy) phenyliminomethylidene} -41 - nitrostilbene (1.94 g, 5.0 mmol) and triethylamine (2.53 g, 25 mmol) in 25 mL of chloroform at 0 under nitrogen atmos­

phere. The mixture was stirred for 24 h at room temperature under nitrogen. The resulting solu­

tion was cooled to room temperature and concent­

rated by distillation of the solvent. The residue dissoved in 60 mL of water, stirred, and filtered with suction. The yellow solid on the filter was washed thoroughly with water to remove salts.

The product was recrystallized twice from etha- nol/acetone (90/10, vol/vol) yielded 1.48 g (65%

yi

d) of pure product 6. Mp 178~180 t： (dec).

lH NMR (DMSO-d6) 8 1.73-2.41 (m, 3H, -CH3-), 3.99-4.57 (m, 4H, -O-CH2-CH2-O-), 5.53-5.78 (m, 1H, vinylic), 5.93~6.20 (m, 1H, vinylic), 6.57—

8.67 (m, 15H, aromatic); IR (KBr) 3018 (w, =C~H), 2963, 2924, 2870 (w, C—H), 1710 (s, C = O), 1618, 1592 (s, C = C), 1505, 1338 (vs, N=O) cm-1. UV /Vis (chloroform) Max=353 nm, £ = 46830. Anal.

Calcd for C27H24N2O5： C, 71.04; H, 5.30; N, 6.14.

Found: C, 71.11; H, 5.25; N, 6.18.

Radical polymerization of 6. A representative radical polymerization procedure was as follows:

In a polymerization tube were placed 0.68 g (1.5 mmol) of 6, 2.5 mg (0.015 mmol) of AIBN, and 3.6 mL of Y-butyrolactone under nitrogen. The re­

sulting solution was degassed by a freeze-thaw process and sealed under vacuum. The polymeri­

zation tube was placed in an oil bath kept at 65

°C. After 24 h the polymer solution was poured into 300 mL of methanol and stirred for 1 h. The precipitated polymer was collected by filtration with suction, followed by washing with 50 mL of methanol. Thus obtained polymer was dried under vacum to give 0.63 g (92% yi

d) of polymer 7.

IR (KBr) 3010 (w, =OH), 2912, 2855 (m, C-H), 1717 (s, C = O), 1613, 1584 (s, C = C), 1502, 1333 (vs, N = O) cm-1. UV/Vis (chloroform) Xmax=353 nm. Anal. Calcd for (C27H24N2O5)/ C, 71.04; H, 5.30; N, 6.14. Found: C, 71.13; H, 5.38; N, 6.22.

Acknowledgement. This work was supported by the Korea Science and Engineering Foundation (951-0305-009-2).

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